In a conventional way of making soybean milk, soybeans must be soaked overnight and are then ground, filtered and boiled. The soybeans tend to deteriorate in quality or even become rancid after having been soaked overnight, particularly in summer. In view that the quality-deteriorated or rancid soybean milk would have adverse influences on the food hygiene, it is tried by the inventor to develop an improved auto-feeding device for food processor, so that soybean milk and other different types of food juice can be made with a food processor in a more convenient and hygienic manner.